The present invention relates to the electronic location and identification of markers. It has particular application to markers used for locating and identifying electrical cables.
The majority of telephony, cable television (catv) and power cables in urban environments are placed underground in duct structures. This is done for reasons of safety, maintenance and aesthetics. The cost of building the underground duct structures is considerable and, as a matter of economics, utilities often share duct space.
Manholes or utility vaults are an integral part of the underground duct structure. They provide a managed space for joining successive lengths of cable and access points to provide communication and power to urban customers. This often results in several cables from various utilities passing through and being jointed in a common vault.
Plant maintenance and service provisioning require clear and unambiguous identification of the cables and joints placed in common areas. In particular, joint boxes or enclosures need to be precisely identified so that a service technician can easily select and enter a designated enclosure. In general, cable enclosures are of similar designs and it is not uncommon to find the same make of enclosure in use on more than one cable at the same vault location. Furthermore, in high density urban environments cable vaults are often located short distances apart to provide frequent access for local service. This often makes difficult the identification of a specific cable and enclosure.
A means for clearly identifying cables and enclosure is highly desirable. One such method is described in U.S. Pat. No. 5,844,405. This employs an electronic marker which is placed in or on the conveyance to be identified. A handheld marker locator is then placed in close proximity to the marker to radiate a radio frequency (RF) signal to the electronic marker. The marker receives the RF signal, converts it to DC power for the internal circuits of the marker, and radiates a secondary RF response signal. This system is similar to RF tags which are used in various applications from identifying products to electronically tagging pets.
This method has an inherent limitation. The RF marker or tag must receive a signal of sufficient field strength to power up the DC circuitry before the marker can respond. This limits the effective range to a few feet or less and, if the marker is shielded by nearby metal, it may not respond at all. Furthermore, the marker responds only with pre-programmed information and can not receive a command to change a condition or request new information.
The present invention in its various aspects addresses these limitations. In preferred embodiments it provides an interactive means to locate and identify underground utilities.
According to one aspect of the present invention there is provided an apparatus for identifying a marker associated with an elongate electrical conductor, said apparatus comprising:
a terminal unit including a power supply for applying electric power to the conductor;
a probe including a probe transmitter and receiver for selectively transmitting an activation signal and for receiving response signals;
a transponder associated with the marker and including:
a transponder receiver for receiving activation signals from the probe,
a response signal transmitter for transmitting response signals to be received by the probe, and
a power supply for receiving electric power from the conductor and for delivering the electrical power to the transponder receiver and to the response signal transmitter.
The transponder is thus powered by the terminal unit over the conductor which may be the metallic shield of a cable, a trace wire or any other available conductor. The power available is not limited to what can be transmitted from the probe so that the range and reliability of the apparatus are considerably extended.
It is preferred that the power be a negative DC voltage, which provides cathodic protection for the conductor. This is especially useful where the conductor is a shield of a buried cable.
According to another aspect of the present invention, there is provided an apparatus for identifying a marker, comprising:
a probe including:
a probe transmitter for selectively transmitting each of a plurality of probe signals, and
a probe receiver for receiving response signals;
a transponder associated with the marker and including:
a probe signal receiver for receiving probe signals from the probe and
a response signal transmitter for selectively transmitting each of a plurality of response signals to the probe and
a processor responsive to receipt of a probe signal by the probe signal receiver to cause the response signal transmitter to transmit a response signal corresponding to the probe signal.
The probe is thus capable of transmitting plural different probe signals to the transponder in order to elicit different responses. This allows the user not only to locate a marker but to identify specific markers and other characteristic information, for example about the marker and the cable or other device with which it is associated.
According to a further aspect of the present invention, there is provided an apparatus for identifying a marker associated with an elongate electrical conductor, comprising:
a probe including:
a probe transmitter for selectively transmitting a radio frequency probe signal;
a probe receiver for receiving radio frequency response signals;
a transponder associated with the marker and including:
a radio frequency probe signal receiver for receiving probe signals from the probe;
a radio frequency transmitter for transmitting radio frequency response signals;
a low baud rate transponder transmitter for transmitting low baud rate command signals on said conductor;
a low baud rate transponder receiver for receiving low baud rate response signals from said conductor;
a processor for converting radio frequency probe signals received by the radio frequency probe signal receiver to low baud rate command signals and causing the low baud rate transponder transmitter to transmit the low baud rate command signals, for converting low baud rate response signals received by the low baud rate transponder receiver to radio frequency response signals and for causing the radio frequency transmitter to transmit the radio frequency response signals.
This provides the user with the ability to query not only the limited information that may be available from the transponder but a much more extensive range of information that can be stored in a terminal unit. Low baud rate signals are used over the conductor to ensure reliability. This is particularly useful where the conductor is a metallic cable shield.
The signal sent to the terminal unit from the transponder may also be used to initiate remote action, for example actuating a remote device. One application is turning on a tone transmitter for cable location purposes.
The low baud rate response signals may include reprogramming code for reprogramming the transponder processor.